Reaction Kinetics, Mechanisms and Catalysis最新文献

In this paper, the reaction network of FTO simplified by kMC was combined in CFD model at bed-scale and whole reaction tube scale. A reaction network consisting of 100 steps elementary reaction of 40 species from DFT was analyzed by kMC to identify the main conversion pathway. The obtained pathway was combined in CFD with a particle-resolved bed model to understand the reaction process. The simulated results showed that increasing inlet temperature increased the net producing rate ratio of ethylene to propylene, decreasing the inlet flow rate reduced the net reaction rate of CO₂. The simulated results of reactor tube scale predicted a STY of 1.55 kg/(L_cat h) of lower olefins, a total CO conversion of 93.5%, selectivity for ethylene, propylene, CO₂ of 7.0%, 43.0% and 50.0%, a hot spot of 619.55 K at 0.1 m from inlet. The total number of reaction tubes would be 3688 for a 200,000 tons per year low olefin plant.

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This study presents a novel approach for synthesizing high-performance Bi₄Ti₃O₁₂ trilayer-doped bio-calcium derived from snail shells using the molten salt technique at 850 °C. Three catalysts were prepared with varying amounts of bio-calcium (Bi_(4−x)Ca_xTi₃O₁₂), where (x1 = 0.05, x 2 = 0.1, x3 = 0.15), it was observed that this activation led to an improvement in properties, the most important of which was an increase in the surface area and a reduction in the gap energy, resulting in excellent photocatalytic efficiency, particularly for biocatalysis with x3 = 0.15. The meticulous engineering of these catalysts gives rise to a synergistic effect, which facilitates efficient charge separation. Moreover, the introduction of bio-Ca led to an expansion in surface area, reaching 4.16, 5.42, and 6.03 m²/g for the bio-Ca/BTO1, bio-Ca/BTO2, and bio-Ca/BTO3, thereby augmenting the catalyst's capacity to absorb, stabilize and photodegradation of Rhodamine-B within a 30 min. Physical and chemical analyses were performed: XRD, FTIR, Raman analysis, BET, MEB/EDX. The bio-Ca/BTO3 photocatalyst’s unique structure enhances its performance and activity by stabilizing and degrading Rh-B on its surface, reducing band gaps, and producing electron–hole pairs. This increased vulnerability to photocatalytic reactions allows for a greater diversity of interactions. The ·OH radical was identified as the most active species in the Rh-B degradation mechanism. The biocatalyst demonstrated remarkable efficacy in degrading the Rh-B dye under visible light irradiation. To assess its stability, an additional eleven repeated simple cycles were conducted. This design offers a novel way to produce high-performance photocatalysts with, an environmentally friendly and sustainable approach.

This study investigates the synthesis of (Cr, Cu)-doped BiFeO₃ perovskites with compositions BiFe_1-x(Cu_x/2Cr_x/2)O₃ (x = 0, 0.1, and 0.2) using the sol–gel method, calcined at 850 °C, to enhance their structural and photocatalytic properties. A comprehensive suite of characterization techniques, including X-ray diffraction (XRD), Rietveld refinement, Fourier-transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), and UV–vis spectroscopy, was employed to analyze the synthesized materials. XRD patterns and Rietveld refinement revealed a phase transformation from BiFeO₃ to Bi₂Fe₄O₉ with increasing Cr and Cu doping levels. SEM analysis showed variations in microstructure, with the average particle size decreasing as Cr and Cu doping increased, reaching a minimum value of 2.355 μm at x = 0.2. The band gap measurements confirmed the successful incorporation of Cr and Cu into the BFO lattice, resulting in a reduced band gap of 2.04 eV at x = 0.2. Photocatalytic performance was assessed by the degradation of Rhodamine B (RhB) under sunlight irradiation. The sample with x = 0.2 demonstrated an impressive 98% degradation efficiency within 180 min, with a calculated rate constant of k_app = 0.01535 ± 0.00122 min⁻¹. This work highlights the potential of (Cr, Cu)-doped BFO perovskites as efficient photocatalysts for environmental remediation applications.

Sol–gel was used to successfully construct a series of silica gel supported Brønsted-Lewis acid ionic liquid (BLAIL/SG) catalysts. The structures of the catalysts were characterized by FT-IR, TGA-DTG, BET, and ³¹P MAS NMR. Meanwhile, the catalytic performance of these series catalysts in the preparation of ethyl laurate was investigated. The results showed that 20%[DMBPSH]⁺(½Cu²⁺)SO₄²⁻/SG catalyst exhibited good catalytic activity in the preparation of ethyl laurate owing to strong Brønsted acidity and the acidic synergy between the ionic liquid (Brønsted), metal ions, and the support (Lewis). A maximum ethyl laurate yield of 94.6% was reached for the 20%[DMBPSH]⁺(½Cu²⁺)SO₄²⁻/SG catalyst under the optimal conditions: ethanol (EtOH)/lauric acid (LA) molar ratio of 5, catalyst amount of 4wt%, time 3 h of reaction at 383 K. After being reused 6 times, the yield of ethyl laurate was still as high as 90.5%, indicating that 20%[DMBPSH]⁺(½Cu²⁺)SO₄²⁻/SG catalyst had excellent reusability. Further kinetic studies showed that the reaction order was 1.15 with activation energy of 25.69 kJ/mol.

Monoclinic BiVO₄ was synthesized by a modified sol–gel technique, using bismuth nitrate pentahydrate Bi(NO₃)₃·5H₂O and vanadium pentoxide V₂O₅ as precursors, dissolved in nitric acid and hydrochloric acid. The prepared samples were characterized by Scanning Electron Microscopy with Energy Dispersive X-ray Analysis (SEM–EDX), Transmission electron microscopy (TEM), X-ray diffraction (XRD), X-ray Photoelectron Spectroscopy (XPS), and UV–Vis Diffuse Reflectance Spectroscopy (DRS). The band gap of BiVO₄ was determined to be 2.53 eV. The Mott-Schottky plot identifies BiVO₄ as a n-type semiconductor with a flat band potential of 0.64 V/SCE and an electron donor density (Nd) of 1.46 × 10¹⁶ (site cm⁻³). Electrochemical impedance spectroscopy confirmed efficient photogenerated electron–hole (e⁻/h⁺) pair separation. Under solar irradiation, BiVO₄ exhibited high photocatalytic efficiency with 96% methylene blue (MB) degradation achieved within 120 min. The photodegradation process is well fitted by a first-order kinetic model, and parameters affecting MB degradation, such as pH and initial concentration, were optimized. A photocatalytic mechanism was proposed in accordance with the scavenger test.

A simple and efficient synthesis of cobalt and zinc spinel ferrite nanoparticles Zn_1−xCo_xFe₂O₄ (x = 0, 0.5) by sol–gel (SG) and co-precipitation methods was successfully developed as a heterogeneous catalyst for styrene oxidation using tert-butyl hydroperoxide as the oxidant and acetonitrile as an effective solvent. The structural properties of the nanoparticles were characterized by X-ray diffraction, Fourier transform infrared, and Raman spectroscopies. Morphological analysis was determined by scanning electron microscopy and energy-dispersive X-ray spectroscopy. The investigation showed that Zn_0.5Co_0.5Fe₂O₄ prepared via the SG method exhibited promising catalytic activity towards styrene epoxide with a conversion rate of 75% and a notable selectivity of 60%. Furthermore, the catalyst demonstrated excellent stability and efficiency after five successive runs. Density functional theory and non-covalent interactions analysis were used to gain deeper insight into the mechanistic aspect.

Novel zirconia supported sodium hexamolybdochromate(III) has been synthesized and used as an efficient catalyst for the synthesis of 4H-benzo[b]pyran derivatives by one-pot three-component condensation of aldehydes, C–H activated compound and dimedone in ethanol at reflux condition. The catalyst was characterized by FT-IR, XRD, EDS, SEM and TGA. EDS analysis explored the pure form of the catalyst, while the XRD pattern indicates that, sodium hexamolybdochromate(III) underegoes in amorphous state. The catalyst is heterogeneous and can be recovered by a simple filtration method. It is reused four times without any major activity loss.

Two kinds of CeO₂/Beta composite catalysts were prepared by precipitation method (CeB-p) and hydrothermal method (CeB-h), respectively. The physicochemical properties of all samples were studied in detail by combining XRD, XPS, SEM, TEM, N₂ sorption, NH₃-TPD and CO₂-TPD techniques. CeB-p catalyst exhibited a higher dimethyl carbonate (DMC) yield than the CeB-h catalyst at the similar conditions for DMC synthesis from CO₂ and methanol. This enhanced activity of CeB-p catalyst was attributed to enhanced acid–base properties modulated by abundant surface lattice oxygen species rather than oxygen vacancies. Compared with the inertly adsorbed methoxy induced by the oxygen vacancy enriched CeB-h, abundant surface lattices oxygen species in CeB-p catalyst facilitated the formation of weakly absorbed methoxy species, which resulted in the shift of the rate-determining step and the reduction of reaction energy barrier. This study offered guidance for the rational design and fabrication of high-performance DMC synthesis catalysts based on CeO₂/Beta composite.

Zinc oxide nanostructures of different morphology were prepared through a facile low-temperature hydrothermal method in the presence of ionic capping agents, cetyltrimethylammonium bromide (ZnO-CTAB) and sodium dodecyl sulfate (ZnO-SDS) and in absence of capping agents (ZnO-1). The synthesis follows an environmentally safer, simpler, and cost-effective method. The present work highlights the morphological transition and its impact on the optical and photocatalytic properties of ZnO nanostructures. Results from X-ray diffraction spectroscopy (XRD) indicate that ZnO is in a single phase with a hexagonal wurtzite structure in all three samples. Photoluminescence spectra showed a green emission mediated by the presence of defects. The UV–vis absorption spectra revealed a marked blueshift in absorbance for capped zinc oxide nanostructures compared to uncapped ones. Raman spectroscopy was carried out to evaluate the vibrational modes of the molecules. FESEM images showed that the morphology changed from nanorods (ZnO-1) to rounded morphology (ZnO-CTAB) and petal-like structure (ZnO-SDS) upon capping with ionic surfactants. Under solar irradiation, the capped nanostructures ZnO-CTAB and ZnO-SDS have effectively decolorized the methylene blue dye compared to uncapped ones and showed improved efficiency. The presence of oxygen vacancies in the nanostructures was confirmed by the emission bands in photoluminescence (PL) studies and by Raman spectral analysis. The synergistic effect of defects in the sample and the morphological transition played an important role in increasing the photocatalytic degradation of the capped ZnO samples. The photocatalytic reaction obeyed pseudo first-order kinetics and the degradation mechanism was investigated using radical scavengers such as tertiary-butyl alcohol (OH radical scavenger), ammonium oxalate (h+ scavenger), and p-benzoquinone (superoxide radical scavenger) to identify the primary species involved in the photodegradation process. The mechanism of photodegradation and the recyclability of capped ZnO nanostructures were studied. The present study suggests the potential of this simple method to prepare desired nanostructures of different morphology using a variety of capping agents that can act as a promising candidate for dye degradation.